The PCB and all its components looked to be absolutely as new and in perfect condition - just couldn’t figure it out. After spending time staring at the PCB, I noticed that there was an unusual fuse holder. I removed the fuse, tested it and found that it was blown. Needless to say, I didn't have any of these tiny fuses in my box of bits, so I ordered some on eBay and waited for them to arrive (from China).
When I replaced the tiny fuse, I powered the amp up again, using a current-limiting power supply, half expecting it to blow again. But it didn’t!
With everything apparently working as it should, I connected it to my IC-705 and a Dummy Load. Dropping the 705’s power to 500mW, I got 20W output from the PA100 into a dummy load. A big smile appeared on my face 😄. I started to increase the power and with a full 5W in, it showed 110W out.
The next step was to connect it to its “natural partner”, the Hermes Lite 2. As mentioned in a previous post, I wanted to take advantage of the ability to run the amplifier output through the Hermes’ Pure Signal processor by adding an RF Sampler.
With the Hermes putting out 750mW the amp was outputting around 25W - perfect (for me).
I went on the 40M band and broke into a QSO between two English operators with booming signals. I was eager to get a good report from them. Sadly, this didn’t quite go to plan 🙄. When I keyed up, I could see distortion on the panadapter and one of the operators told me my audio was indeed badly distorted.
Without any idea what was causing the distortion, I removed the RF Sampler and tried again. This time, the outgoing signal looked perfect and so I recontacted the operator I’d spoken with moments ago. He confirmed that everything sounded fantastic. He told me that there were some Linearity settings in Thetis which would probably resolve the issue.
Sitting there, I wondered if it was simply a case of there not being enough attenuation in the sampler’s coupling output (-50dB), therefore overloading the HL2’s Pure Signal input 🤔. I’d need to add some inline attenuators and experiment more. But that’s for another day - I don’t want to detract from the performance of the amplifier.
I didn’t have an interface lead and since I’m going to be selling this amp, I can’t see the point in making one, so I used the band-sensing and it worked amazingly well - faultlessly even!
The amp also has RF-Sensing which means that you don’t need to fit a PTT SEND line - just transmit and the amp instantly detects the RF. It works well, but I’d still recommend fitting a lead between the two devices. The menu has options for Icom, Yaesu and Xiegu protocols.
Unlike say a Xiegu XPA125, the PA100 doesn’t have an ATU so I connected an LDG Z-100Plus. Now this would present a problem in that initiating a tune could mean the amp could potentially see huge amounts of reflected power and very high swr during the tune-cycle (it will protect itself if it sees anything greater than 2:1). Thankfully, the PA100 has a BYPASS mode which is accessed by a simple press of the Function button. Once the ATU has found a match, it’s just a case of pressing the Function button again.
There’s an impressive amount of protection built into the amp which keeps an eye on high swr, and high temperature - there are two fans fitted in a push-pull arrangement. The fans are quick to switch on and although they aren’t noisy, you are certainly aware of their presence.
There’s also that tiny 20A fuse which protects from over current and even from applying the power supply the wrong way around (I am so pleased that the previous owner wasn’t aware of the existence of the fuse) 😂🤣😂.
The front panel sports just two things a screen and a button! The display is pretty small but extremely clear and easy to read, providing all the information you need. The (function) button switches between PA ON and PA OFF (bypass) and also gives access to other functions. It’s a little odd, but you soon get used to it. The only thing that concerns me about it is that it sometimes doesn’t detect a press which can be annoying. It also makes me question the longevity of the button.
Other than that button though, I must admit that the construction of this cheap Chinese amp is absolutely excellent!! The pcb seems to be a high quality item and the components look to be very well soldered and carefully placed. There’s not even a hint of “cheap tat” that you often get with these budget devices. Everything looks top notch.
 |
| Note the huge heatsink |
CONCLUSION
Putting aside the fact that I got this amplifier for a ridiculously low price, I have to say that the Micro PA100 is a great little amp, brimming with features, versatility and safety.
If I needed a 100W amp, then I wouldn’t hesitate to invest in one of these. They can be used with virtually any transceiver, without the need for an interface lead and you’d have to be an idiot to do it any harm (sorry previous owner).
Its compact dimensions and light weight mean it can easily be taken on POTA outings. It’s just a great little all-rounder. For a Foundation License holder, I like the fact that you can transmit under a Watt and get a solid 25 Watts, giving both radio and amp an easy life.
Before I sell it, I’m going to resolve the RF Sampler issue, just because I want to understand what the cause is.
Thanks for visiting the blog!
73, Tom, M7MCQ.
No comments:
Post a Comment